Glycogen Metabolism Flashcards
_____ is the major storage form of CHO in the body
Glycogen, found in liver, muscle (some in brain)
- Reaction: Glucose → Glucose-6-Phosphate (GLYCOGENESIS)
Starting Compound: Glucose
Ending Compound: Glucose-6-Phosphate
Enzymes: Glucokinase or Hexokinase
- Reaction: Glucose-6-Phosphate → Glucose-1-Phosphate (GLYCOGENESIS)
Starting Compound: Glucose-6-Phosphate
Ending Compound: Glucose-1-Phosphate
Enzymes: Phosphoglucomutase
- Reaction: Glucose-1-Phosphate → Uridine Diphosphate (UDPGluc) + Pyrophosphate (GLYCOGENESIS)
Starting Compound: Glucose-1-Phosphate
Ending Compound: Uridine Diphosphate (UDPGluc) + Pyrophosphate
Enzymes: UDPGluc Pyrophosphorylase
Process of Glycogenolysis
In the cytosol (muscle & liver), glycogen is broken down to glucose
_____ (catalyzes the rate-limiting step in glycogenolysis) & cleaves 1,4 glycosidic bonds
Glycogen phosphorylase
(1/2) Debranching enzyme has two catalytic sites. ______ moves a trisaccharide from one branch and places it on the other branch so the 1,6 branch point is visible.
Glucan tranferase
(2/2) The second catalytic site of debranching enzyme, _____, is responsible for catalyzing the hydrolysis of the alpha 1-6 glycolytic bond that releases a free glucose.
1,6-glycosidase
Reaction: Glucose-1-Phosphate → Glucose-6-Phosphate → ????
Free Glucose
Glucose-6-Phosphate is found in _____ & ____
Glycolysis (Glucose → Glucose-6-phosphate, Glucose-6-Phosphate → Fructose-6-Phosphate)
Glycogenesis (Glucose → Glucose-6-Phosphate, Glucose-6-Phosphate → Glucose-1-Phosphate)
Glucose-1-Phosphate is found in _____ & _____
Glycogenesis (Glucose-6-Phosphate → Glucose-1-Phosphate, Glucose-1-Phosphate → Uridine Diphosphate (UDPGluc) + Pyrophosphate)
Glycogenolysis
- Glycogen synthase & Glycogen phosphorylase regulation
o Phosphorylation of synthase (synthase-stop) = ↓ activity
o Phosphorylation of phosphorylase = ↑ activity
Glycogen synthase during glycogenesis
o ↓Phosphorylation
o cAMP ↑ phosphorylation; thus ↓ glycogen synthase
o Insulin ↓ cAMP ; thus ↑ glycogen synthase (glycogenesis)
Glycogen phosphorylase during glycogenolysis
o ↑ phosphorylation
o cAMP ↑ phosphorylation; thus ↑ glycogen phosphorylase
o Insulin ↓ cAMP ; thus ↓ glycogen phosphorylase (glycogenolysis)
_____ increases the phosphorylation of enzymes
Cyclic AMP
Cyclic AMP is formed in response to ____, _____ & _____
epinephrine, norepinephrine (muscle & liver), glucagon (liver)
Role of glycogen in the liver
provide free glucose to maintain blood concentration of glucose
Role of glycogen in muscle
provide a source of G6P for glycolysis in response to ATP need for muscle contraction.
- Phosphorylation → Phosphorylase a = active
a. Glycogen phosphorylase activated by phosphorylation catalyzed by phosphorylase kinase to yield phosphorylase a
b. Allosterically inhibited by ATP and G6P in liver not muscle.
- Dephosphorylation → Phosphorylase b = inactive
a. Glycogen phosphorylase inactivated by dephosphorylation catalyzed by phosphorylase kinase to yield phosphorylase b.
CHO Loading
Endurance athletes exercise to the point of exhaustion to deplete glycogen stores. Then, they consume an excess of carbohydrates to replenish glycogen stores, glycogen synthesis happens rapidly due to the lack of glycogen. This new glycogen is then used as a readily available source of fuel during intense exercise.
